The objective of the studies described in this Proposal is to determine the influence of plasma membrane composition on immune recognition. We have chosen as a model system the recognition of H-2K and H-2D gene products by antibody and by cytotoxic T lymphocytes (CTL). Our experimental approach involves reconstitution of highly purified H-2K and H-2D glycoproteins in lipid vesicles of defined chemical composition. We will measure thermodynamics and kinetics of binding of antibody and CTL to these vesicles. Antigen density and lipid composition will be varied systematically, and the effects of such changes on binding will be determined. Binding of antibody-coated lipid vesicles to a macrophage-like cell line will be studied similarly. The studies outlined in this Proposal will serve as a prototype for defining molecular events in immune recognition of cell surface proteins. We will measure binding as a function of vesicle/effector cell concentration, binding as a function of temperature, and kinetics of binding at constant temperature. Results of these studies will be used to test molecular models of vesicle-cell or vesicle-antibody interaction.